[llvm] [Coroutines] Only rematerialize when operands are available after the suspend (PR #209195)

[Christian Ulmann via llvm-commits]

Dinistro wrote:

> Net cost in frame size is `(bytes for all values introduced by doing the rematerialize - bytes for rematerialized value)`, we could decide to rematerialize if this net cost is negative.
> 
> alignment demands make this calculation more complicated though.

I deliberately decided to not use byte sizes of values for simplify. This could be added, if we want to make this more powerful.

https://github.com/llvm/llvm-project/pull/209195